Chatting

Question

I want to develop online chatting in Windows Application using C#.net
some problems i am facing are...

1.How do i check, the Users who are signed in  / signed out of the application. (Signed in UserName should be populated in ListView and Repeatedly checked who are online / offline Users, Offline users name should be removed from ListView)

2.Is it possible to send / Receive Method in same windows Application & Which Protocol  to be used. (Selected UserName from Listview to whom we want to send a message, IPAddress of UserName is tracked and Message can be Sent, but not able to Receive  Message to that user.)